This application relates in general to ATM systems, and in specific to a mechanism for monitoring and displaying ATM traffic loads by bit rate service type.
ATM or asynchronous transfer mode is a data communications standard or protocol that allows the delivery of data packets or cells to and from different network elements. An ATM network allows for the use and transfer of multiple types of data, e.g. constant bit rate, and variable bit rate. Thus data such as frames, packets, video data, voice data, file data, etc. can be transmitted over the ATM network. The ATM protocol organizes data into cells, which are similar to data packets but comprise standard format with a standard length. Each ATM cell is 53 bytes in length, 5 bytes of which are the header, with 48 bytes of data.
The ATM network is a pipeline that comprises a plurality of communication channels. Each channel has a specific quality of service designation or type, with the higher quality channels costing more than lower quality channels. In this instance, higher quality means higher delivery reliability. During periods of high traffic volume, high quality channels will maintain their bandwidths and thus will not lose their cells, while low quality channels will have their bandwidths reduced, and cells may be lost.
There are three service types for channels defined by ATM. The highest quality service type is the constant bit rate or CBR service. This service type is used for data which must be delivered at a constant rate, such as telephone, sound, or video, or else the data transmission would be corrupted. The next lower level service type is the variable bit rate or VBR service. This service type is used for data which may be delivered in bursts and where timing between cells is not critical, such as file transfers. The lowest quality service type available is the ABR service. This service fills the remaining bandwidth in the ATM network pipe after allocation for CBR and VBR services.
A problem with the ATM specification is that it does not provide for any comprehensive network management beyond a policing mechanism, which is used to ensure that a particular customer does not exceed their allocated bandwidth. The policing mechanism tracks the cell usage rate for a particular customer. Network customers contract with the network management for a particular bandwidth at a particular type of service. For example, a customer may be granted 5% of the pipe bandwidth with a CBR service type. Thus, the policing function tracks the cell usage to ensure that this customer never exceeds their allocated bandwidth. Note that the policing mechanism usually tracks both burst usage and cells per second usage. A burst limit restricts the number of cells that can be transmitted back-to-back, whereas cells per second represents an average over a time period. However, this limited mechanism does not provide a network manager with an adequate characterization of network performance.
Therefore, there is a need in the art for a ATM management mechanism that provides a network manager with information about network traffic over time.
These and other objects, features and technical advantages are achieved by a system and method which monitors ATM traffic load by service type.
The inventive mechanism receives each cell being transported over the ATM network, and determines relative numbers of cells of each of the service types with respect to the total bandwidth of the network.
The inventive mechanism is a real-time data collection protocol analyzer. The mechanism maintains a network table wherein each customer connection or channel in an particular ATM backbone link is identified as to its type of quality of service, i.e. CBR, VBR, or ABR. The mechanism forms the table by monitoring signaling channel cells, in particular connection/call setup-request cells (request for service cells) and their associated connection call answer cells (acknowledgment cells) during service negotiations. In these cells, the service type is identified for each customer channel, wherein each channel is denoted by a Virtual Path Identifier/Virtual Circuit Identifier (VPI/VCI) tag in the header of each cell. The mechanism also tracks the number of cells per second for each of the identified VPI/VCI tags. The mechanism then groups the VPI/VCI tags according to each type of service and thus, can determine and display the manner in which the entire bandwidth of a particular pipe is used by service type.
The inventive mechanism may utilize alarm levels for each aggregate traffic type or group of types. For example, an alarm could be set to trigger if CBR exceeds 20% of available pipe bandwidth.
Therefore, it is a technical advantage of the present invention to monitor ATM network traffic by service type.
It is another technical advantage of the present invention to determine trends in traffic usage of the network to permit upgrade forecasting.
It is a further technical advantage of the present invention to maintain a table, in real time, that lists VPI/VCI tags, along with the service type and bandwidth usage for each tag.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.